This invention relates to coffee and more particularly to a coffee percolation process wherein soluble coffee solids are extracted from roasted and ground to produce a coffee extract which is further processed into a dry, reconstitutable soluble coffee powder.
Percolation is the semi-continuous countercurrent extraction of soluble coffee solids from roasted and ground coffee. The extraction process is performed in a percolator set which is a series of extraction columns, generally 4 to 6. At steady-state operation, the extraction columns contain roasted and ground coffee of varying degrees of extraction. An aqueous extraction liquid, generally water, is fed at elevated temperatures to the entrance of the extraction column containing the most extracted coffee in the percolator set, typically referred to as the spent stage extraction column. The extraction liquid passes through this column extracting soluble coffee solids from the coffee contained therein, exits this column, and is passed to and through the next successive extraction column containing the next most extracted roasted and ground coffee in the percolator set. In a similar manner the extraction liquid is passed through successive extraction columns containing progressively less extracted or fresher roasted and ground coffee extracting soluble coffee solids therefrom. Finally, the extraction liquid is passed through the extraction column containing the least extracted roasted and ground coffee in the percolator set (generally fresh, unextracted roasted and ground coffee). This column is typically referred to as the fresh stage extraction column. A pre-determined quantity of extraction liquid is drawn-off from this column as coffee extract, thus completing a cycle, which is then further processed to produce a dry soluble coffee product. The coffee extract will typically contain between 20 percent - 35 percent soluble coffee solids by weight.
A new cycle is begun by taking the spent stage extraction column from the previous cycle off stream and placing an extraction column generally containing fresh unextracted roasted and ground coffee on-stream thus becoming the fresh stage extraction column for draw-off of coffee extract for this cycle. Aqueous extraction liquid is then fed to the spent stage extraction column for this cycle, the coffee contained therein being the next most extracted coffee in the previous cycle, and the process continues as before with extraction liquid passing through extraction columns containing progressively less extracted roasted and ground coffee and finally being drawn off as coffee extract from the fresh stage extraction column.
In this manner, then, a given bed of roasted and ground coffee becomes progressively more extracted with each cycle. (Cycle being defined as the period between successive draw-offs of coffee extract from the fresh stage extraction column.)
An understandably important consideration in the coffee percolation art is to maximize the yield of soluble coffee solids obtained from a given charge of roasted and ground coffee. Unique to percolation, however, is the desire to avoid impairment of the characteristic flavor and aroma constituents of coffee so that the final soluble coffee product will more nearly resemble freshperked roasted and ground coffee. This factor often must often be balanced against yield maximization. Thus, for example, the use of extremely high temperatures, while useful in achieving high yields, is to be avoided since it will significantly impair and alter the delicate flavor and aroma characteristics of the coffee.
While numerous advances have been made in the art in achieving relatively good yields without substantially affecting product quality there exists a recognized need for further improvement in this area.